Synchronizing system



NOV- 9, 1937- F. scHRTl-:R 2,098,598

SYNCHRONIZING SYSTEM Filed Nov. 21, 1952 INVENTOR. fe/rz fr arf# TTORNEY Patented Nov. 9, 1937 UiTD STATES ATNT OFFIQE SYNCHRONIZING- SYSTEM tion of Germany Application November 21, 1932, Serial No. 643,596 In Germany December 12, 1931 2 Claims.

The present invention relates to an arrangement for synchronizing cathode ray picture recorders or re-creators.

It is known in the prior art that cathode-ray oscillographs, that is, Braun tubes, may be used for picture transmission, especially for the purposes of television and tele-cinematographic work by controlling the brightness of the cathode ray spot upon the fluorescent screen of the tube from the sending end as the ray spot passes from one point to the next, while the spot at the same time passes over the picture eld along a series of adjoining lines. This latter motion must be synchronized with the identical decomposing or scanning process of the picture to be sent out from the transmitter end, and must also be maintained at the proper phase therewith. It is known in the art that for this purpose what is known as Kipp or relaxation waves locally generated at the receiving end may be used, and these are kept in step by the aid of impulses transmitted by the sending outfit. The invention represents a simple embodiment of such a spotcontrcl scheme.

The basic idea of the invention consists in that, in the process of picture transmission a short interval is interposed after each line in the course of which the transmitter sends out the synchronizing impulse designed to keep the oscillograph at the receiving end in step, and that ways and means are provided whereby this impulse intended to release the line control action for the picture-re-creating spot may be distinguished from the sending impulses resulting from the scanning of the picture itself. For this purpose the device or tube provided for the purpose of controlling the instantaneous position of the cathode ray pencil, such as a television (glow) lamp, glow relay, thyratron, multi-electrode tube, connected in parallel relation to the condenser becoming charged up in the course of a picture-line is blocked until the cathode ray beam has reached the end of the picture line.

A short while later, a line-electrode located approximately in the plane of the picture screen and extending over the whole length or height of the picture (straight wire or the like) is negatively charged by the punctiform impinging electron stream and thus by the aid of a plate current blocking the relaxationcircuitpften referred to asa tilting circuit, the latter is caused to be released. The shift-ing of the spot at right angles to the direction of the picture line advance or feed may be controlled by the aid of an independent arrangement of a similar type of the simplest possible kind manually re-adjustable in a ready manner, for instance, by the aid of a glow-lamp, condenser and charge or leak resistance that is an ohmic resistance or electron tube working inside saturation current. feasible to make the period and phase of the second control arrangement functionally interdependent with the arrangement controlling the line-motionor the correctiveimpulses of the transmitter whenever very exact and stable picturepoint distribution is required.

One embodiment of the apparatus of this invention is represented by the drawing. Referring to the latter, numeral i stands for the Braun tube serving for the re-creation of the picture with the picture eld 2 indicated by the dash-box, the picture being built up from constituent lines by the cathode ray beam or spot developed within the tube, with the lines running, for instance, in the direction of arrow 3. All elemental areas are covered by the cathode ray in the same sense and direction as is peculiar to the present type of control. The transmitter apparatus for this purpose may operate also with a cathode ray oscillograph, though mechanical scanning means would be likewise permissible provided they insure a suitable scanning motion. Suitable forms of mechanical scanning devices could be the well known Nipkow disc, the mirror wheel, and similar systems.

In either case, according to the spirit of this invention, a brief interval must be interposed after each line of image for the generation and transmission of the corrective impulse. `In rder that special means may be dispensed with at the sending end, recourse most simply may be had to the method predicated upon the so-called blank-margin method whereby the corrective impulse is produced photo-electrically. The dash-line 4 indicates the position of the cathode ray beam at the beginning or origin of the image; for its space movements deflecting plate pairs 5, 5 and 1, 8, are used as known in the earlier art. The plates, if desired may be replaceable also by magnetic coils or solenoidsr. The assumption is made for the purpose of this disclosure that the pair of plates '1, 8 controls the line feed; the second circuit arrangement hereinbefore mentioned and required for the said purpose shall not be discussed in this connection. One electrode of each control system designated by 6 and l in the drawing is united by the junction wire I6 with the direct current source I3 of the plate, said connection being established at a point which in reference to the diaphragmlike anode 9 presents an adequately high nega-V Of course, 'it is also A tive potential suflicient in order to preclude disturbances in accurate deflection of the spot as a result of charge actions produced inside the tube due to ionization of residual gases. For the tapping of the lead brought to plates 6 and I recourse may be had, if desired, also to a potentiometer arrangement.

The cathode II in the present instance, consists of a directly heated lamentary wire provided with an electron-emissive coat and being fed from an alternating current supply line or network by way of a transformer I2, it being understood that the use also of indirectly heated cathodes would fall inside the scope of this invention. The Wehnelt cylinder I0 serving for brightness control, that is, concentration control, is supplied with a suitable negative biasing potential from the direct current source of potential I4 by way of the modulation resistance I5. In order that additional action may be brought upon the initial position of the spot from the outside, recourse is had to a permanent magnet I'I, for instance, which is positioned in a suitable place in reference to the tube I. For more exact adjustments recourse may suitably be had to an adjoining magnet either of a permanent or electro-type laid around the tube and having suitable pole arrangements. Anode 9 is grounded at 33.

The forms of electrodes as hereinbefore described by reference to the drawing, of course, will have to be chosen in accordance with the state of the art. For instance, Wehnelt cylinder I0 need not necessarily have this form, indeed, it may be replaced also by a conveniently disposed diaphragm, a ring, a wire network or gauze, or equivalents; Also, the shape of the anode 9 and of cathode II may be varied at will, and finally also supplementary auxiliary grids, such as screen-grids, are imaginable with the end in view of improving the conditions surrounding the brightness or light control or the space control or of rendering the same more sensitive.

For brightness control recourse is had to the following scheme:

The radio frequency Vcurrents picked up by thev radio receiver I9 are amplified and demodulated; the audio frequency current variations amplified in the power amplifier 20 which correspond to the scanned brightness intensities in the transmitted picture are conducted by way of the modulation resistance I5 where they cause the potential variations impressed upon the Wehnelt cylinder I0 and which by way of the concentration changes of the electron beam modulate the brightness or intensity of the spot in the picture field 2.

For the purpose of controlling the line motion the following arrangement is employed: In parallel relation to the modulation resistance I5, at the output end of the power amplier 20, there is provided a high resistance 26 through which the rectified picture current is passed. The adjustable condenser 22 which is included in the shunt to the controller plates 5 and 6, at the beginning of each picture line is charged up from the direct current source I3 by way of lead I6 and the very high resistance 2I with the result that owing to the growth in potential Ydifference across plates 5 and 6 the cathode ray spot travels through its linear motions. Y

The voltage, capacity and resistance data of this circuit are so chosen that operation is inside the practically linear part of the charge sistance 26.

curve of the condenser 22. As a consequence, the spot will travel along the lines at a constant rate of velocity. This behavior is made possible by the partial voltage taken oil" at the direct current source I3 by Way of lead it being very high compared with the maximum potentialrequired between plates 5 and 6. This shows that the arrangement must be brought to the tilting point a long while before the full charge of condenser 22. What is used therefor is a controlled glow-type relay or some suitable kind of hot-cathode thermionic tube arrangement; this arrangement preferably consists here of a gaseous space discharge device 23 or in other words a vapor electric device provided with a hot filament, a plate electrode 24 and control grid 25. By the anode current of amplifier tube 28 and by the aid of the fall of potenial occasioned across the resistance 2l, the said grid becomes subject to a negative blocking potential. Only when an adequately high positive potential is impressed upon the control grid 25 will the discharge gap between plate and hot cathode of the gaseous space discharge tube 23 be caused to respond and charge con-denser 22 and the pair of plates 5, 6, connected in parallel relation thereto will be charged to the Very low rupture potential of the gas gap. This positive control or unblocking potential, however, can be supplied to the tube 23 only by a supplementary fall of potential across resistance 26'which is traversed both by the rectified picture current as well as the corrective current impulse transmitted at the end of each picture line.

Care must be taken according to this invention so that the unblocking of the gaseous space discharge device 23 and thus the tilting of the arrangement will not be caused in the course of a picture line by the sending impulses produced at bright elements of the image. For this purpose there is employed the linear electrode I8 disposed with the Braun tube along the margin of the picture consisting, for instance, of a straight insulated wire arranged a short distance in front of the screen surface. As long as the said wire I8 is not struck by the cathoderay beam a suitably adjusted normal current will flow through the amplifier tube 28 comprising the control grid 2S and the plate-current source 3D. The drop of potential occasioned as a result across the resistance 2l is chosen so high that even in the presence of maximum impulses of the picture-telegraph transmitter the potential of the gaseous space discharge device control electrode 25 will never become positive by opposite action across the terminals of re- But if upon completion of a picture line the wire i8 is impinged by the Ideflected beam of electron-rays the control grid 29 of tube 28 will momentarily be charged to a high negative value, the iiow of the plate current will be blocked in 28, and the fall of potential across resistance 2'I as a consequence becomes zero. As a result the corrective impulse transmitted by the sending equipment after the end of the picture line, by virtue of the positive potential set up thereby across Vthe terminals of resistance 26 and imparted to the control electrode 25, becomes active in shock-like fashion. The gaseous space discharge tube 23 thus is caused to respond and because of its high permeability to or transmission of current, the capacities 22 Vand 5, 6, are discharged practically instantaneously with the result that the spot is caused to 1 jump back to the starting point of the next line.

After this has been accomplished, renewed charging o-f 22 and of 5, 6, begins; but before a potential difference has been built up between anode 24 and the heated filament of the gaseous space discharge tube 23 sufcient to resume the discharge, grid 29 of the tube 28 has become sufficiently discharged by way of leak resistance 3i so that normal current can flow again and that the fall of potential across resistance 2l takes care of the blocking of the thyratron. In order to adjust the time-constant of the blocking means, an adjustable co-ndenser 32 is provided.

It will be noticed that the equipment hereinbefore disclosed involves only a limited number of means inasmuch as all that is required for line-control is a simple inexpensive hot cathode tube of minimum power (28) and a small gaseous space discharge tube (23) which is also inexpensive to make. The shift o-f lines, as has been shown, is insurable also by simple means such as a glow-lamp, condenser, and charge-resistance of charge-tube. It would also be possible to insert for this object another condenser which upon each discharge impulse of the gaseous space discharge device 23 experiences the same small growth in charge. This condenser may be imagined as being connected in parallel to the plates 1, 8. At the end of the entire picture, by the agency of another similar gaseous space discharge device, glow-relay, or the like, and which is lmade to respond only to a special synchronizing impulse produced after a complete picture re-creation, the transverse deflection condenser parallel to 'l and 8 may be discharged. In order to insure selective response to this particular sending impulse the same may be transmitted, for instance, by the aid of a frequency outside the picture modulation and convenient receiving lters. 'Ihis arrangement would be a substantial duplicate, except for a different time constant, of that shown for the rapid deflection and to simplify the drawing is not therefore illustrated.

Having now described my invention what I claim isz- 1. In a television system a cathode ray tube, means for defiecting the cathode ray developed within the tube, said means comprising a condenser and means for uniformly charging the condenser, a gaseous space discharge device normally biased below cut-olf and operable at predetermined time periods to discharge said condenser, said means for biasing the gaseous space discharge device below cut-oli comprising a no-rmally operative amplifier tube having in its output circuit a resistor the voltage drop through which is adapted to bias the control electrode of the said space discharge device, an electrode element provided within the cathode ray tube and subjected at points of maximum sweep of the cathode ray pencil to the electron stream of the said pencil, a connection between said electrode and the input circuit of said amplifying A means for dei'lecting the cathode ray developed within the tube, said means comprising a condenser and means for uniformly charging the condenser, a gaseous space discharge device normally biased below cut-off and operable at predetermined time periods to discharge said condens.

er, said means for biasing the gaseous space discharge device below cut-01T comprising a normally operative amplifier tube having in its output circuit a resistor the Voltage drop through which is adapted to bias the control electrode of the said space discharge device, an electrode element provided within the cathode ray tube and subijected at points ci maximum sweep of the cathode ray pencil to the electron stream vof the said pencil, an electrical connection between said electrode and the input circuit of said amplifying device whereby during time periods when said electrode is subjected to the influence of the electron pencil a negative bias voltage is supplied to the amplifying tube to produce a state of inoperativeness thereof, and resistor means connected with the input circuit of the said space discharge device and the output circuit of said amplifying tube, said received signals representing predetermined normal times of completion of the sweep circuit and being adapted to flo-w through said resistor whereby the voltage drop produced thereby opposes the control of the said space discharge device by said amplifying tube so as to bias the space discharge ,l

tube to cut-olf independently of the operation of the amplifying tube and thereby discharge the storage element to cause the beam to return to a starting position.

FRITZ SCHRTER. 

